Field of the Invention
The present invention relates generally to fan blades for gas turbine engine fan assemblies and, more specifically, metal leading edges for fan blades.
Description of Related Art
Aircraft turbofan gas turbine engines include a fan assembly having a plurality of circumferentially spaced apart fan blades extending radially outwardly from a rotor disk. Ambient airflow is channeled between the blades and pressurized thereby generating thrust for powering the aircraft in flight. The fan assembly typically includes a plurality of circumferentially spaced apart fan blades each having an airfoil attached to a dovetail root disposed in a complementary, axially extending dovetail groove or slot in a perimeter or rim of a rotor disk or drum. The airfoil may be attached to the dovetail root by a shank. A spinner is mounted to a front end of the fan assembly to provide smooth airflow into the fan as illustrated in U.S. Pat. No. 6,416,280, by Forrester et al., entitled “One Piece Spinner”, which issued Jul. 9, 2002.
In order to make engines more efficient, there are efforts to decrease the fan blade radius ratio (RR) which is a ratio of inner fan flowpath diameter/outer flowpath diameter and which indicates how much airflow can be passed through the engine. A smaller radius ratio (RR) results in a larger flow area, and better performance. As the fan blade radius ratios decrease by moving the fan platform flowpath surface inboard towards an engine centerline or axis, the fan blade leading edge profile along the airfoil and a portion of the shank begins to become larger and abrupt. RR may be decreased by increasing the outer fan diameter or making the inner flowpath and inner flowpath diameter smaller which is preferred. Increasing the overall fan diameter is less desirable because it increases drag.
Maximizing a low radius ratio design results in the blade LE profile along the airfoil and shank being more exposed to the aerodynamic flow path. This exposed LE needs to be protected from erosion as well as birdstrike damage. In addition, flatness of the exposed shank leading edge portion is an aerodynamic drag penalty during operation resulting in a fuel consumption penalty.
Thus, there is a need to protect areas of the fan blades shank that are exposed to airflow, erosion, and birdstrike. There is also a need to reduce aerodynamic drag of the exposed flat leading edge of the fan blade shank.